1. Field of the Invention
The present invention relates to preventing corrosion in cooling tower systems and, more specifically, to preventing corrosion or tuburculation of carbon steel and other corrosion prone materials subjected to contact with cooling tower water contaminated with hydrocarbons and/or sulfides.
2. Description of the Prior Art
Cooling towers are widely used in the refining and petrochemical industry to cool water used in heat exchangers, refrigeration units, etc. Commonly, the cooling tower systems employed in such environments are of the recirculating type, such that the water is used for cooling purposes and recycled to the cooling tower for chilling. It is common, particularly in refinery operations, for the cooling tower water to become contaminated with hydrocarbons, sulfides or both. These contaminants pose a special problem in controlling corrosion because of the fact that the hydrocarbons tend to form coatings on the corrosion prone materials inhibiting the action of the corrosion inhibitors and, at times, chemically reducing some of the active inhibitor components, while sulfides, which are generally severely corrosive in virtually any environment, can cause deposits leading to deep pitting or tuburculation.
Anti-corrosion compositions which employ various zinc compounds, molybdates, polyphosphates, etc. are well known. Examples of such compositions may be found, for example, in U.S. Pat. Nos. 4,217,216; 4,176,059; 4,017,315; DE No. 2,850,925 and Japan Kokai JP No. 52/38438 (77/38437). Additionally, an article entitled "Molybdate as a Pipeline Corrosion Inhibitor for Coal-Water Slurry Systems," Phys. Metall. Res. Lab., 1986, discloses a composition comprised of molybdate, zinc sulfate and potassium phosphate as an erosion-corrosion inhibitor for steel used in coal-water slurries.
In addition to the above prior art, the composition disclosed herein has been used as a corrosion inhibitor in so-called clean water cooling tower systems, i.e. cooling tower systems wherein the water is generally free of contaminants, such as hydrocarbons and/or sulfides.